The present invention relates to a method for the preparation of a diamond-clad machining tool or, more particularly, to a method for the preparation of a machining tool having a cladding layer of diamond formed by the method of chemical vapor-phase deposition.
As is well known, diamond is the most useful and preferred to various kinds of carbide-based cemented hard alloys as a material of tools for machining such as cutting, lathing, shaping, planing and milling, of which extremely high hardness and wearing resistance are required. Diamond materials conventionally used in machining tools include polycrystalline sintered bodies of powdery diamond and natural and synthetic single crystals of diamond and they are all suitable as a material of machining tools by virtue of their extremely high hardness and wearing resistance as well as excellent resistance against welding to the workpieces under machining.
In addition to the above mentioned conventional diamond materials, several attempts and proposals have been made recently to prepare a diamond-clad machining tool by utilizing the so-called chemical vapor-phase deposition method in which a thin film of diamond is deposited from the vapor phase as a cladding layer on the base body of a machining tool made of a metal or a cemented carbide so as to give a diamond-clad machine tool. Such an attempt hitherto undertaken is not successful to manufacture diamondclad machining tools useful in practical machining works.
One of the serious problems in the preparation of a diamond-clad machining tool by the method of chemical vapor-phase deposition is that a sufficiently high adhesive bonding strength can hardly be obtained between the vapor phase-deposited film of diamond and the surface of the base body of the tool made of a metal or a cemented carbide. Moreover, this problem is more serious when the cladding layer of diamond has a larger thickness. For example, exfoliation of the cladding layer of diamond readily takes place when a cutting tool having a cladding layer of diamond deposited on a base body of a cemented carbide is used in cutting work.
Another problem in the chemical vapor-phase deposition of diamond in the prior art method is that the selection of the material forming the base body on which diamond is deposited is limited because the efficiency of the vapor phase deposition of diamond is greatly influenced by the kind of the material. For example, the efficiency of deposition of diamond is very low on a base body of iron, steel or other ferrous alloys so that diamond-clad machining tools can hardly be prepared by use of such a base body.
Moreover, the cladding layer of diamond formed by the chemical vapor-phase deposition method has a rough surface especially when the diamond layer has a relatively good crystallinity so that machining tools having a cladding layer of diamond as deposited have limited application fields as a wear resistant tool. Accordingly, lapping of the diamond surface as deposited is sometimes indispensable in order to increase the surface smoothness of the cladding layer. The lapping work naturally reduces the thickness of the cladding layer sometimes by 10 .mu.m or more so that the diamond layer as deposited must have a thickness so much larger than necessary in the finished tool after lapping while, as is mentioned above, the bonding strength between the cladding layer of deposited diamond and the base body of to tool is decreased as the thickness of the cladding layer is increased, for example, to exceed 10 .mu.m.